
where \(r_i\)  (\(i=1-9\) ) and \(c_{11}\)  denote the quartic couplings in 3HDM with the \(Z_3\)  symmetry defined in Ref. [1]}.
The criterion that the partial wave amplitudes satisfy the unitarity is given by
\(|\Lambda _{i}|<8\pi .\) 
